The invention relates to an ultrasonic actuator device, comprising in particular a movable actuator arm arrangement and at least one ultrasonic driver unit, which is arranged for driving the actuator arm arrangement by acoustic streaming. Furthermore, the invention relates to an operational instrument, e. g. a medical instrument, like an endoscope, a biomedical device for minimally invasive surgery, and/or a catheter, or a mechanical machine apparatus, comprising at least one ultrasonic actuator device. Furthermore, the invention relates to methods of using the ultrasonic actuator device. Applications of the invention are available e.g. in the fields of miniaturized actuators, micro actuators, wireless machines, measuring devices, and medical endoscope technology. Further applications include wireless control of tools and machinery.
For describing the background of the invention, particular reference is made to the following publications:    [1] Faulhaber: Brushless DC-Micromotor 0206, Data sheet (http://www.u-motor.com.cn/BL-motorF/PDF/0206.pdf);    [2] D. K.-C. Liu et al. in “Acoust. Sci. & Tech.” 31:2, 115-23 (2010);    [3] U.S. Pat. No. 5,770,913;    [4] S. Yokota et al. in “Journal of Robotics and Mechatronics” 17:2, 142 (2005);    [5] A. H. Epstein. in “Proceedings of ASME Turbo Expo 2003” Atlanta, Ga., USA, Jun. 16-19, 2003;    [6] US 2013/0271088 A1;    [7] U.S. Pat. No. 6,272,922 B1;    [8] A. Denisov et al. in “Journal of Microelectromechanical systems” 23: 3, 750-9 {2014);    [9] U.S. Pat. No. 8,147,403 B2;    [10] A. Hashmi et al. in “Lab on a chip” 12: 4216-27 (2012);    [11] R. J. Dijkink et al. in “J. Micromech. Microeng.” 16: 1653-9 (2006);    [12] J. Feng et al. in “MEMS 2013”, Taipei, Taiwan, Jan. 20-24, 2013;    [13] J. Feng et al. in “MEMS 2014”, San Francisco, Calif., USA, Jan. 26-30, 2014;    [14] U.S. Pat. No. 5,906,579 A;    [15] M. Ovchinnikov et al. in “J. Acoust. Soc. Am.” 136: 1, 22-9 (2014); and    [16] N. Nama et al. in “Lab on a chip” 14:15, 2824-36 (2014).
The miniaturization of motors and machines that perform a mechanical task is extremely challenging, but important as could for instance enable minimally invasive biomedical devices for in vivo diagnostics and surgery. Currently, miniaturization of micro machinery is hindered by the size of the available actuators and the control and electronics that is needed to operate them. Electromagnetic motors, which work at larger scales (with diameters larger than about a centimeter), are difficult to miniaturize to below one millimeter. One of the smallest commercial electromagnetic motor is 1.9 mm in diameter and 6 mm in length [1].
In recent years, researchers therefore developed new miniaturized actuators, including electrostatic MEMS (Micro-electro-mechanical-system) motors, an electro-conjugate fluid motor, piezoelectric motors, pneumatic actuators, and a MEMS gas turbine engine [2-5]. The size of these actuators is much reduced compared with traditional actuators. However, a drawback common to all of these actuators is that they are all connected to complex wire connections or tubes to provide the power and to control the actuation. This problem limits the application of these actuators, and means that their overall size is also bigger. Multiple degrees-of-freedom are essential in positioning or steering miniaturized machines. Actuators for multiple degrees-of-freedom require an increasing number of wires (or tubes) as the degree-of-freedom increases, as besides the power additional control cables are needed, which dramatically increases the complexity and rigidity of the connections, and eventually causes operational problems if the device is too small. This means that the overall diameter of the device is at least several millimeters, whereas applications for endoscopes for instance require smaller diameter devices.
Ultrasound has been proposed to transfer power wirelessly [6-7]. However, these approaches convert mechanical vibration to electricity using the piezoelectric effect and then utilize the electricity to power a device. This electricity conversion process adds additional complexity and suffers from low efficiency.
Denisov et al. reported a mechanical system that is remotely excited by ultrasound and converts acoustic energy into motion using a receiving membrane coupled with a discrete oscillator [8]. In that case, the energy conversion relies on the resonance of the solid membrane, thus a large area and a restricted shape are required for the device. This disadvantage can be overcome through the conversion of ultrasonic energy directly to mechanical motion via acoustic streaming, as proposed in [9-13] and the present specification. Advantageously, mechanical motion by acoustic streaming does not require conversion to electric power.
It is well known that oscillating bubbles in fluids can cause acoustic streaming. Many microfluidic pumps and mixers are based on this phenomenon [10]. It was shown by Dijkink et al. that an oscillating bubble in a tube can be used as an ultrasonic actuator for turning a cantilever arm at centimeter scale [11]. Recently, a sub-millimeter scale “swimmer” in a microfluidic channel was propelled by the same mechanism as reported by Feng et al. [12-13]. However, these publications have been described for investigating the acoustic streaming mechanism only. The propelled components are not practically usable as actuators in terms of limited movability, e.g. on a circle [11], and limited usable driving force. Yet another approach uses a capsule device for in vivo sensing that is propelled by acoustic streaming [9]. However, the streaming is based on an on-board energy storage in the capsule, resulting in a limited miniaturization capability.
From an application point of view, current endoscopes with small overall diameter, as are for instance used in urology, only have one bending section near the tip of the endoscope with only one degree-of-freedom. Magnetic catheter steering was reported and used in clinics [14], but all the magnets are under the same magnetic field, thus it is unable to address individual actuators through magnetic approach. Thus, due to restrictions of actuator mechanisms, conventional medical instruments have restricted applicability.
Other mechanical machines, like current robot arms for operation in inaccessible environments, suffer from the large size and complicated structure of current actuators, thus have restricted applicability as well.
An objective of the invention is to provide an improved ultrasonic actuator device, which is capable of avoiding limitations and disadvantages of conventional techniques. Furthermore, methods of using the ultrasonic actuator device are to be provided. In particular, the objective of the invention to provide the ultrasonic actuator device having a simple structure, improved miniaturization capability, improved integration capability and/or reduced complexity of power supply and control. It is a further objective of the invention to provide an improved operational instrument, e.g. a medical instrument and/or a mechanical machine apparatus, which is capable of avoiding limitations and disadvantages of conventional techniques. In particular, the operational instrument is to be provided with extended functionality and applications.
The above objectives are solved by an ultrasonic actuator device, an operational instrument and a method comprising the features of the invention.